Dry electrical recording medium



DRY ELECTRICAL REfiORDlNG MEDIUM i Robert S. Schwartz, Great Neck, N. Y., assignor to Faximile, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application May 18, 1953, Serial No. 355,843

6 Claims. (Cl. 204-4.)

This invention relates to recording media of the type which are subjected to an external application of heat to render the medium markable electrically.

While not limited thereto, the invention is particularly useful in the art of electrical recording wherein it is desirable to pass a recording current through a conductive record medium containing an electro-responsive marking compound. In recorders operating on this principle, the recording current is applied to two cooperating electrodes, and a conductive sheet or tape, which may be impregnated paper or cloth, is drawn between the electrodes. Marks are made on the conductive medium by electro-chemical change.

Paper, being White and inexpensive, is very desirable for record purposes. However, paper is normally nonconductive and must be impregnated with suitable chemicals to make it electroconductive and suitable for use in electrical recorders. Perhaps the most successful of the recording papers in use at the present time is the type impregnated with an aqueous electrolyte and a marking compound such as disclosed in patent to J. V. L. Hogan et a1. 2,339,267. This paper is eminently suitable for most recording applications but has the characteristic that it must be maintained with the proper moisture content during storage until actually recorded on by record ing apparatus.

Another type 'of electrographic' recording paper is known, and is disclosed in patent to R. B. Gibney, 2,530,956. This type of paper is fabricated as a composite sheet of several layers. One layer, the recording layer, is impregnated with a solid compound consisting of acetamide alone or in combination with propionamide or formamide. Another layer is impregnated with the same amide or amides and an ionizable organic dye, the ions of which migrate to the recording layer when the solid impregnant is melted, by the passage of an electric current therethrough, to produce a characteristic mark. In recording paper of this type there is the disadvantage that at least two layers are required to form the composite sheet. The acetamide which forms the basic impregnant suhlimes or evaporates readily at normal ambient temperatures and pressures so that the paper must be stored in a sealed container to remain operative. At ambient relative humidities exceeding 85% the paper becomes soft, weak, sticky and wrinkled because the amide content is extremely hygroscopic. The high humidity renders the paper unmanageable in conventional recorders and markability becomes either impaired or impossible.

Applicants purpose has been to provide a dry, white recording medium employing a single layer sheet or tape of paper or cloth impregnated with one or more suitable amides, an ionizable salt, and an electro-responsive substantially colorless marking compound. The recording medium is markable only by being first externally heated and then subjected to a suitable electrical voltage between electrodes, one of which may be an element having an nited States Patent iron content. The recording medium is characterized by its extreme stability under conditions of high humidity and prolonged exposure to theambient atmosphere.

It is therefore a principal object of the invention to provide a dry recording medium which can be rendered conductive only by external heating and is then electrically markable.

It is a further object to provide a white, dry, single layer porous recording medium impregnated with an amide which is a hydrogen substitution product or derivative of acetamide, an ionizable salt, and a substantially colorless electro-responsive marking compound.

It is a further object to provide .a white, dry recording medium which is rendered electroconductive only when externally heated and which remains wholly stable and markable under all humidity conditions.

It is a further object to provide a dry recording medium which is electroconductive and electrically markable when externally heated and which retains its markability 0n prolonged exposure to ambient atmospheric conditions.

It is a further object to provide a dry recording medium impregnated with a solid amide which does not require special packaging for storage prior to use.

It is a further object to provide a novel impregnant composition for a recording medium.

For a description of a recording apparatus and method suitable for the recording medium of this invention reference is had to my copending application Serial No. 102,136, filed June 29, 1949.

Generally the invention contemplates a recording medium such as paper or cloth impregnated with one or more amides, a highly ionizable salt, and a substantially colorless electro-responsive marking compound. The combination of amide and salt is hereinafter designated as a composite electrolyte. The composite electrolyte is normally solid, substantially non-hygroscopic and nonsubliming or non-evaporative under normal ambient conditions. it includes as one ingredient a substitution prodnot of acetamide (CHsCONHz), having a melting point above 20 deg. C. where substitution is at the alpha carbon atom.

Quite unexpectedly it was discovered that certain substitution products of acetamide are for the purpose of this invention considerably superior to acetamide and other primary amides of the form .R-CO-NHz. Since one object of the invention is to provide a substance which is solid, dry and substantially non-subliming or non-evaporative at ordinary ambient temperatures, amides having a low melting point were found not suitable. Formamide is an example of such an unsuitable primary amide since it is a liquid at ordinary temperatures and subject to evaporation on exposure. Acetamide, another primary amide, has also proven to be unsuitable since it is subject to extreme sublimation or evaporation on exposure and is objectionably hygroscopic in high humidity ambient conditions. Compositions of acetamide with propionamide and acetamide with formamide known in the prior art have been found to be similarly subject to sublimation or evaporation and are objectionably hygroscopic.

As a general rule normally solid primary amides which are hydrogen substitution products of acetamide Where substitution is at the alpha carbon atom have been found satisfactory as ingredients of the composite electrolyte of the present invention since they are dry, solid, and substantially lnon-subliming or non-evaporative at normal ambient atmospheric conditions. Among these amides are those of the forms CHzXCONl-Iz, CHX2CONH2 and CXsCONHz, i. e. CH(n-3)XnCONH2, where X is the substituted group and n is an integer from 1 to 3. There:

arsesor CHzXCONl-lrz Chloroacetamidc Iodoacetamidc Cyanoacetamide Fluoroacetamid e Bromoacetamide Hydronyacetam.

CHXECONHZ Dichloroacetamide Fluorobrcmeacetam' Difiuoroacetamide Chlorobromoacet.

C C H Trichloroacetamide Dichlorofluoroacetamide Trtbromoacetamide Dichlorobromoacctamide Trifiuoroacetamide There is one derivative of acetamide, nitroacetamide, which decomposes at 8 deg. C. above its melting point. This characteristic so limits its usefulness that is must be regarded as generally unsatisfactory for the present invention. it is possible however, to use nitroacetamide in the present invention if it is mixed with a major quantity of other derivatives of acetainide.

In addition to an amide of the types described, the normally-solid composite electrolyte of this invention includes a highly ionizable salt. Numerous highly ionizaable salts can be used, such as. for example, sodium nitrate, potassium nitrate, ammonium nitrate, ammonium chloride, ammonium sulfate, and Sodium chloride. These salts are not to be taken as limiting the invention which is applicable generally to all highly ionizable salts both inorganic and organic. It will be understood that with cc"- tain ot' the salts better results will be obtained with some of the amides than with others. and for a particular use some combinations will be found better than others. Commercial grades of amides may contain enough salts as impurities to provide clectroconductivity and it will be understood that the use of such impure grades falls within the scope of the present invention.

The composite electrolyte may be formed by melting the selected amide and adding a relatively 51 .all amount of the salt. Or the amide and the salt may be dissolved in an appropriate common solvent which may then be removed by evaporation leaving the dry, white composite electrolyte. i

In mak'ng a dry recording medium which, at elevated temperatures, is markable responsively to electric currents, a suitable clectro-responsive marking compound is added with the salt to the molten amide. Electra-responsive marking compounds as contemplated herein are generally substantially colorless compounds which depend on electro-chemical action to change to dark colors; examples of these are catechol and pyregallol. Catechol and pyrogallol are normally white crystalline lake-forming compounds and turn black when in liquid electrolyte and subject to electric current from an iron electrode having a positive polarity. Other suitable electro'responsive marking compounds are known in the tut.

it may be pointed out that as regards the combination of an amide, a salt and a specific marking conpound, tr e chemical nature of the marking compound should be alien into consideration and combinations se ected which have characteristics appropriate to the requirements of the particular application involved. it will be noted that use of a colored marking dye embodied in a separate layer of the marking sheet as known in the prior art is undesirable in the present invention, since a single layer white porous recording medium is required. T e composite electrolyte and the substantially colorless marking compound of the invention impregnate the entire r cording paper. By this arrangement it becomes possible to use a single layer sheet of paper as the entire recording medium. A further advantage of combining a substantially colorless marking compound with the composite electrolyte is that manufacture of the recording paper is simplisince a single dip in the proper solution lmprcgnates the paper.

The following example is intended as illustrative of one way in which the invention can be demonstrated.

Example I A solution may be made by heating 10 g. of chloroacetamide with 0.1 g. of potassium nitrate until molten. About 0.2 g. of catechol is added to the hot solution. A piece of absorbent paper stock is immersed into the hot so ution, blotted to remove the excess melt and allowed to cool. The resulting sheet will be White and apparently dry. The dry impregnated paper sheet may then he placed on a metal plate connected to one terminal of a -volt D.-,C. source. The other terminal may be connected to a stylus containing iron. When the stylus is touched to and drawn over the paper no mark will be made. The metal plate may then be heated to about .30 deg. C. whereupon the dry impregnated paper will assume a wet appearance. When the stylus is now touched to and drawn over the paper, intense black marks will be left on the paper.

The invention can be demonstrated as described in Example I with any of the acetamide derivatives heretofore listed employing any of the ioni z able salts and an 1;- ing compound above mentioned. in order to demonstrate the scope of the invention samples of dry recording paper were made employing certain other primary amides not derivatives of acetamide. It was found that these recording media were inefiective, unstable, or had other objectionable characteristics as discovered in the tests described below. Samples of impregnated recording paper prepared as described in Example 1 were formulated as follo Sample A:

Acetamide 20 g. Potassium nitrate 0.3 g. Catechol 0.3 g.

Sample B:

Acetamide 20 g. Propionarnide 2 g. Potassium nitrate 0.3 g. Catechol 0.3 g.

Sample C:

Acetamide 20 g. Formamide 2 g. Fotassiurn nitrate 0.3 g. Catechol 0.3 g.

In addition samples of recording paper were prepared as described in Example I each including at least one of the derivatives of acetamide heretofore listed. All samples of recording paper were tested as follows:

rns'r non rrroaoscorrc nrrrnc'rs All samples of recording paper were placed in a closed humidity test chamber having a relative humidity of least at 20 deg. C., and atmospheric pressure. After one hours exposure in the test chamber the samples were removed. The papers containing acetamide derivatives were all slightly limp from moisture absorbed by the paper but they were all smooth to touch and unwrinkled. These papers were then heated on a hot plate to l30 de C. and were tested for markabili'ty as in Example 1. Black marks were produced on all the acetamide derivative papers when an iron electrode wa touched to and was drawn over the papers.

The papers containing acetamide were soft, sticky. weak and wrinkled from absorbed moisture when removed from the humidity test chamber. The acctarnide papers were heated on a hot plate to deg. C. tested for marlgability as in Example. I. The marks produced when an iron electrode was touched to or drawn over the papers were irregular, spotty and objectionably light.

TEST FOR EFFECTS OF PROLONGED EXPOSURE Samples of paper containing derivatives of acetamide as well as papers containing acetamide formulated as listed in samples A, B and C were exposed to normal varying ambient atmospheric conditions for a period of twenty days. Each sample was then heated on a hot plate at 130 deg. C. and tested for markability at 45 volts as in Example I. Black marks were produced on all paper samples containing derivatives of acetamide when an iron electrode was touched to and was drawn over the papers. No mark was produced on any of the sample papers containing acetamide. It was found that the amide content of these papers has sublimed or evaporated to the extent that no marking was possible when tested for markability at 45 volts in accordance with the method of Example I.

OBSERVATIONS AND CONCLUSIONS The above tests clearly demonstrated that the physical condition of the papers containing substitution products or derivatives of acetamide were substantially unaffected by conditions of high humidity and of prolonged exposure to varying ambient atmospheric conditions, and their markability, when tested in accordance with Example I by externally heating and then applying an electrical voltage was unimpaired. It was furthermore found that the amides in these papers sublimed or evaporated to such a small extent under all humidity and storage conditions that the markability of the papers was not impaired. The papers containing either acetamide, a combination of acetamide with propionamide, or a combination of acetamide with formamide were all extremely hygroscopic under highly humid conditions, becoming too soft, weak, wrinkled, and sticky to be handled practicably in recording devices commonly used in the art. Under conditions of prolonged exposure to ambient atmospheric conditions the amide content of the acetamide papers sublimed or evaporated to the extent that marking by external heating and application of an electrical potential in accordance with Example I was not possible.

Of the amides found satisfactory as ingredients of the composite electrolyte for use in this invention, it will be noted that all were substitution products of acetamide as heretofore defined. Of the amides found unsatisfactory, none was a substitution product of acetamide.

It must be emphasized that it is essential to the invention that the amide content of the recording medium be such that the recording medium will remain operative upon prolonged exposure to varying ambient atmospheric conditions. Thus the rate of sublimation or evaporation of the amides is a critical factor to be observed in selection of suitable amides for the impregnant. Of the amides found satisfactory for the purposes of the present invention, all have an inherent vapor pressure less than that of acetamide. The rate of sublimation or evaporation is of course directly related to the inherent vapor pressure. Thus it may be regarded as essential to the present invention that amides selected as ingredients of the impregnant according to the present invention have an inherent vapor pressure less than that of acetamide. It is also essential to the invention that none of the amide impregnants have a melting point less than 20 deg. C.

This application is a continuation-in-part of my application Serial No. 102,135, filed June 29, 1949, now abandoned.

I claim:

1. A dry white recording medium which is initially substantially non-conductive electrically, comprising a single layer porous member impregnated with an electroresponsive substantially colorless marking compound, a highly ionizable salt, and a major quantity of an acetamide derivative having the form CH(3-7L)X1LCONH2, Where X is a substitution group, and n is an integer from 1 through 3 inclusive, the acetamide derivative being selected from the group consisting of cyano-, fluoro-, chl0ro-, bromo,- iodo-, and hydroxy acetamides, said medium being rendered electroconductive and electrically markable when the impregnant is heated to the melting point thereof.

2. A dry, white, impregnated recording medium, which is initially substantially non-conductive electrically and which becomes electroconductive and electrically markable only when heated above the melting point of the impregnant thereof, comprising a single layer porous member impregnated with a highly ionizable salt, an electroresponsive substantially colorless marking compound, and a non-subliming acetamide derivative, said derivative having the form CH(3n)XnCONH2, where X is a sub stitution group and n is an integer from 1 to 3, said derivative being selected from the class consisting of cyano-, hydroxy-, and halo-acetamides.

3. A dry, White recording medium according to claim 2, wherein said acetamide derivative has the form CH2XCONH2.

4. A dry White recording medium according to claim 2, wherein said acetamide derivative has the form CXsCONHz.

5. A dry, white impregnated recording medium, which is initially substantially non-conductive electrically and which becomes electroconductive and electrically marl:- able only when heated above the melting point of the im pregnant thereof, comprising a single layer porous member impregnated with chloroacetamide, a highly ionizable salt, and an electroresponsive substantially colorless marking compound.

6. A dry, white, recording medium comprising a single layer porous support impregnated with an ionizable salt, a colorless lake-forming compound and a non-subliming acetamide derivative having the form CH(3-n)XnCONH2, where X is a substitution group and n is an integer from 1 to 3, said derivative being selected from the class consisting of cyano-, hydroxy-, and halo-acetamides, the impregnant rendering said support initially substantially nonconductive electrically and rendering the support electroconductive and electrically markable only when heated above the melting point of the impregnant, said impregnant in the melted state being stable during the marking of said support.

References Cited in the file of this patent UNITED STATES PATENTS 168,466 Edison Oct. 5, 1875 2,339,267 Hogan et al. Jan. 18, 1944 2,421,367 Soloman May 27, 1947 2,440,526 Soloman Apr. 27, 1948 2,530,956 Gibney Nov. 21, 1950 

1. A DRY WHITE RECORDING MEDIUM WHICH IS INITIALLY SUBSTANTIALLY NON-CONDUCTIVE ELECTRICALLY, COMPRISING A SINGLE LAYER POROUS MEMBER IMPREGNATED WITH AN ELECTRORESPONSIVE SUBSTANTIALLY COLORLESS MARKING COMPOUND, A HIGHLY IONIZABLE SALT, AND A MAJOR QUANTITY OF AN ACETAMIDE DERIVATIVE HAVING THE FORM CH(3-N)XNCONH2, WHERE X IS A SUBSTITUTION GROUP, AND N IS AN INTEGER FROM 1 THROUGH 3 INCLUSIVE, THE ACETAMIDE DERIVATIVE BEING SELECTED FROM THE GROUP CONSISTING OF CYANO-, FLUORO-, CHLORO- BROMO, IODO-, AND HYDROXY ACETAMIDES, SAID MEDIUM BEING RENDERED ELECTROCONDUCTIVE AND ELECTRICALLY MARKABLE WHEN THE IMPREGNANT IS HEATED TO THE MELTING POINT THEREOF. 